A semiconductor chip is usually sealed with a resin for shielding and protection from outside air, and mounted on a substrate as a molded product called a package. For sealing a semiconductor chip, a curable resin such as a thermosetting resin such as an epoxy resin is used. As the method for sealing a semiconductor chip, for example, a so-called transfer molding method or compression molding method is known wherein a substrate having a semiconductor chip mounted thereon is disposed so that the semiconductor chip is positioned at a predetermined location in the cavity of a mold, and a curable resin is filled into the mold and cured.
Heretofore, a package is molded as a package molded article for each chip which is connected via a runner which is a flow path of a curable resin. In such a case, a mold release film may sometimes be used for the purpose of improving releasability of the package from the mold.
The mold release film is useful also with a view to preventing sticking of a curable resin to the mold. However, in the sealing step of a semiconductor element, even if a mold release film is disposed, there is a problem such that gas (outgas) and a low viscosity material generated from the curable resin will pass through the mold release film and will be in contact with the high temperature mold to contaminate the mold. If the mold contamination occurs, it is obliged to stop the sealing process of the semiconductor element in order to clean the mold, whereby production efficiency of the semiconductor package is reduced. In recent years, there have been advances in making the curable resin used for sealing to have a lower melt viscosity or to be a liquefied resin, whereby the above problem is more likely to occur.
In order to prevent the mold from contamination by outgassing, etc. from the cured resin, a mold release film having a metal foil or a vapor-deposited film of metal or metal oxide provided as a gas barrier layer, has been proposed (Patent Documents 1 to 3). Further, a mold release film having a resin film with high releasing property and a resin film with high gas barrier property (an ethylene-vinyl alcohol copolymer film, etc.) laminated, has been proposed (Patent Document 4).